Electrodeposition of nickel using an untreated anode



United States Patent Office Bidifihh Patented Dec. 22, 1%64 3,162,586 ntncrnonnsosrriou or rooster. canto AN uurnnarsn anions;

Donald H. Schantz, Grand assigncr to Mlichigan Plating d; tainping 30,, Grand Rap-i Mich, a corporation of Bel-aware No Drawing. Filed duly 16, 1962, 32. No, Elli, Z4 4 Claims. (@l. Edd-4%) This is a continuation-in-part of my copending application entitled Electrodeposition, Serial No. 860,735, filed December 21, 1959, now abandoned.

This invention relates to a solution to be used in electrodeposition and to a new and improved method of electrodeposition. More particularly, this invention relates to a new and improved nickel plating solution enabling the use of substantially pure, and relatively inexpensive nickel as the anode, and the method of nickel platin using this solution and anode.

The nickel plating solution now in common use is known as the Watts solution. The development of the Watts bath or solution was a milestone in the nickel plating art and variations of this solution are still thought to be the best electrolytic solution for the electrodeposition of nickel. The Watts bath is therefore old and wellknown in the art and is comprised of nickel sulfate (NiSOgl-EO), nickel chloride (NiCl -6H O) and boric acid (HgBGg). The function of the nickel s ate is to supply the required nickel ion for'electrop The function of the nickel chloride is to assure eflicient dissolution of the nickel anode. The role of the borlc acid is that of a boiler, to assure cat the pH of the solution remains substantially constant. T

his is the basic solution used today in the electrodeposition or nickel, the concentrations of the various ingredients being varied with pH, temperature, current density and amount of agitation.

Many attempts have been made to improve the Watts solution so that substantially pure nickel would corrode uniformly and gradually in a satisfactory manner as an anode when used in the solution. Such nickel is considerably less expensive than the cast or rolled nickel presently in use. Presently, controlled amounts of carbon and silicon are combined with the nickel, or the nickel is highly oxidized, or it is formed with sulfur combined therewith or one of several other materials. These materials are actually activators since before the present discovery, no one, as far as it is known to the inventor, has been able to use substantially pure relatively inexpensive nickel as anode material Without bagging and o ler precautions. Such nickel, for example, is free of carbon, silicon, etc. and is normally used for forming steel alloys. It may be obtained by the hydrogen reduction method or by electrolyzing methods. One result of uneven corrosion of the anode is loose nickel particles. One attempt was to raise the chloride concentration and thereby decrease the amount of loose nickel formed at the anode. However, all chloride solutions still produce loose nickel and do not change the fundamental type of corrosion at the anode. thers have heat treated electrolytic nickel to improve its performance as an anode. Although this is an improvement, the anode still corrodes in a manner producing an etched surface on the anode and a residue of loose nickel. Therefore, all attempts presently known to use electrolytic or other pure nickel as an anode in the Watts solution have left much to be desired.

Consequently, cast or rolled anodes are commonly used commercially, because when such anodes aresub jected to the electrolytic and corrosive effects of nickel plating baths, less loose nickel is produced at the anode. Since loose nickel produced at the anode in all probability will find its way to the article being plated at the cathode, the article will not be properly plated since these particles Will produce a rough nickel deposit. As stated previously, the use of cast or rolled nickel anodes reduces the amount of loose nickel deposited in the bath, however such anodes are much more costly than elec trolytic nickel.

Another approach to the problem of loose nickel being produced at the anode has been to use bags of various types which supposedly catch all loose nickel produced. Cast or rolled carbon bearing nickel anodes find the Widest use commercially. The fraction of a percent of car bon contm'ned in these anodes produces during use a carbon film on the anode surface which normally holds back most of the nickel particles until they have dissolved. Generally a cloth bag is used to hold back the carbon film. However, the bags sometime break or are ripped during use, suddenly setting free large amounts of carbon and nickel particles in the plating solution causing the nickel deposit at the cathode to be rough. If the cloth bag is of a heavy tightly woven material the nickel solution inside the bag becomes too concentrated and the anode does not dissolve or corrode properly. if the bag is made of a light, loosely, woven material, the carbon and nickel particles may Work through the bag. Thus, the selection of material for the anode bag is essentially a compromise and hence not completely satisfactory. Therefore, the anode bagging approach is also unsatis factory because of the costs involved and because a practical bag has not been found which collects all of the loose nickel from an improperly corroded anode. Consequently, the expensive nickel compounds and mixtures are still used for the anode.

Presently, efforts are being made in the industry to use electrolytic nickel by placing pieces into a titanium basket. This is relatively expensive, cumbersome for dellcate plating, and not overly satisfactory since much loose nickel is produced and bags are required.

It is therefore an obiect of this invention to provide an electrolytic solution for the electrodeposition of nickel together with a method of nickel plating which makes it possible to use inexpensive substantially pure nickel as an anode, without necessitating the usual additives as activa- I tors.

Another object of this invention is to produce such a solution and provide such a method whereby a substantially pure nickel anode corrodes evenly and uniformly.

In use, it has been found that the anode remains smooth. and semi-bright with no noticeable loose nickel being produced.

Another object of this invention is to provide a plating solution which will be useful where chloride and boron free deposits are desired at the cathode, since the novel bath and method do not contain either chloride ions or boric acid.

Another obiect of this invention is to provide such a solution which still has simplicity of composition, good bullering and the ability to plate rapidly.

Still another object of this invention is to provide a method of electrodeposition of nickel wherein it is not necessary to bag the anode.

These and other objects of this invention will become obvious to those skilled in the art of the electrodeposition of nickel upon reading the following specification.

My novel nickel plating solution actually departs radically from the conventional Watts bath. The only real similarity is that nickel sulfate is used as the principal source of nickel as in the Watts solution. However, neither nickel chloride nor boric acid are used, nor desired. Rather, a compatible fluoride salt is added to the solution so that fluoride ions are present therein. It has been found that at least about 3 ounces per gallon of solution is required in order to use pure nickel as the anode. This will vary slightly with the pH of the solution. The best results are obtained when using nickle fluoride. Potassium fluoride can be used in some circumstances as well as sodium fluoride, although these latter'two are not preferred in "most instances since they cause some hardening of the plate. Mixtures thereof can'also be used. Ammonium fluoride is not a suitable fluoride salt since the ammonium ion causes undue hardness and brittleness of the plate. The presence of ammonium ions in concentrations of 0.1 oz. per gallon or greater is untenable. The presence of fluoride ions in the plating bath produces excellent anode corrosion, the anode remaining smooth and semi-bright with no noticeable loose nickel being produced. Since fluoride salts are strong buffers, they serve the dual purpose of providing excellent anode corrosion and buffering the solution against rapid changes in pH. 'Hydrofluoric acid may also be used under some circumstances to provide the fluoride ion, however, the pH must be adjusted by the addition of nickel carbonate or nickel hydroxide, etc.

The addition of fluorides to a nickel plating bath is not entirely new since attempts were made as early as 1961 V 'to'addsmall amounts of fluorides to the Watts solution.

However, no benefit was found from adding small amounts of fluorides to a solution containing boric acid, since the boric acid reacted with fluorides to produce fluoborates, the fluoborates reacting much differently in the solution than the fluoride ion. However, I discovered that when fluorides were added to a nickel sulfate and boric acid solution so that all'of the boric acid was used in reaction therewith,'upon further addition of fluorides to the solution, the plating quality increased. Next, the boric acid and borates were eliminated altogether and just the specific fluorides were added in the required amounts as stated previously. A marked change in the anode corrosion was noted. Such changes had never been noted heretofore. Upon experimentation it was found that the fluoride ion in the specific electrolytic solution. produced this result. It Was found that the concentration of fluoride ion necessary in the solution dependson the'temperature, pH, anode current density and the amount of agitation in the solution, with 1 at least about 3 ounces per gallon being required under I normal operating conditions.

Lower concentrations 'of fiuoride ion are required when high bath temperatures are used, when the pH value is lowered, when the anode current density is lowered and when the agitation is increased.

t was found that large pure nickel anodes could be used,

'not pieces as heretofore required. The following are examples demonstrating results and advantages of my invention. Pure nickel anodes thus worked very well, indeed, such as electrolytic nickel anodes having no added special ingredients. 1 No titanium basket is necessary to make the pure nickel anode operative. In fact, such a basket would dissolve in the present bath.

' It should be understood that the term substantially pure? nickel primarily designates nickel having no special additives according to usual practice to make it suitable as a plating anode. Of course, certain minor impurities are always present to some'degree. In other words, the "nickel may be ordinary indoctored nickel produced by 'any'desirable process such as hydrogen reduction or electroylsis or the like.

Example 1 1 When the'anode or electrolytic, substantially pure'nickel The anode remained smooth and semi-bright, and very little or no loose nickel produced.

Example, 2

Upon using a solution composed of 300 g./l. nickel sulfate (NiSO -6H O) and 45 g./l. nickel fluoride (NiF -4H O) at a temperature of F. and an anode current density of 20 amps. per sq. foot, excellent anode corrosion was obtained at a pH up to 4.0 with moderate agitation. It is advisable that chlorides be substantially absent from the solution since a very small amount of nickel chloride will change the smooth semi-bright appearance of the anode to a rough pitted surface like that normally obtained from a Watts solution. Since boric acid reactswith fluorides to produce fluoborates and since fluo'borates do not produce the same e'ffect at the anode as fluorides, it is also preferred that boric acid and borates be excluded from the solution. However, if boric acid is present, enough soluble fluoride may be addcxl to convert the boric acid present to fiuoborate and an additional amount added to provide the desired amount of fluoride ions necessary for fairly, good anode corrosion at the desired operating conditions.

The pH of this bath should not be allowed to go much above 4 since it is not eifective at higher pH. Practical operating conditions dictate a low pH of about 1.5-2. It has been found that the optimum pHwithin this range will vary depending upon the concentration of ingredients, temperature, current density, and agitation. Such a solution provides a wide range of operating conditions under which high anode efliciency may be obtained. In addition to the unique type of anode corrosion obtained from a bath containing fluoride ions, the nickel deposit produced at the cathode has some unique properties since it is chloride and boron free. An important advantage of such a solution is the fact that lower priced nickel without additives may be used as an anode. Such a solution has good buffering and is extremely simple in composition. Only two ingredients are necessary while three are used in the Watts solution. It has the ability to plate rapidly. It will permit the use of cast or rolled nickel anodes of higher purity than presently used since it does not require the carbon film found on such anodes required when the Watts solution is used.

One of the most serious problems connected with nickel plating today is that of poor distribution of the nickel deposit on the complex shapes being designed to be plated. This situation can be improved in two ways with this solution. One improvement is through the use of bipolar or auxiliary anodes which do not require bagging as previously and the other is through the use of this solution in combination with the process of reversing the current at intervals of, for example, five minutes of plating andabout minute to 3 minutes of reverse current at the same or a different current density. By reversing the current when using this solution, more nickel is deplated from the areas where it is thickest, resulting in a deposit of greater uniformity. Since the nickel anode corrodes smoothly, the deposit nickel will corrode smoothly also in the fluoride solution when the'current is reversed. Not only may a deposit of greater uniformity of thickness be produced, but a deposit result which is smoother than the base metal upon which it is plated will be produced. This is called leveling and is now only obtained commercially through the use of organic additives.

Another advantage of this solution is its less corrosive nature compared with the Watts solution for many metals. While it is true that the sulfate-fluoride solution will corrode glass, nevertheless it is somewhat less corrosive to stainless steels'cornpared with the ordinary chloridecontaining Watts nickel plating solution.

Another advantage of this solution is its greater toler- I ance for some metallic impurities.

Due to the solubilizing and complexmg ability of the fluoride ion, the metallic impurities are tied up in soluble but only slightly ionized fluoride salts. Thus, they are held in solution instead of precipitating and slowly plate out with the nickel being deposited.

The above description has been for the purposes of illustration and description and not by way of limitation. All changes and variations are to be included within the spirit and scope of this invention unless the following claims expressly state otherwise.

I claim:

1. A method of electroplating nickel comprising the steps of: forming an aqueous bath consisting essentially of nickel sulfate; 21 fluoride salt selected from the group consisting of nickel fluoride, potassium fluoride, and sodiurn fluoride, and mixtures thereof; immersing into said bath an anode of substantially pure untreated electrolytic nickel, immersing into said bath the article to be plated as the cathode; and electroplating said article from said pure nickel anode.

2. A method of electroplating nickel comprising the steps of: forming an aqueous bath consisting essentially of nickel sulfate; a fluoride salt selected from the group consisting of nickel fluoride, potassium fluoride, and sodium fluoride, and mixtures thereof; and being substantially free of chloride ions and boric acid; immersing into said bath an anode of substantially pure untreated electrolytic nickel, immersing into said bath the article to be plated as the cathode; and electroplating said article from said pure nickel anode.

3. A method of electroplating nickel comprising the steps of: forming an aqueous bath consisting essentially of nickel sulfate; nickel fluoride of a concentration to cause fluoride ions to be present; and being substantially free of chloride ions and boric acid; immersing into said hath an anode of substantially pure untreated electrolytic nickel, immersing into said bath the article to be plated as the cathode; and electroplating said article from said pure nickel anode.

4. A method of electrodepositing nickel which comprises electrolyzing a substantially pure untreated electrolytic nickel anode in a solution consisting essentially of nickel sulfate and nickel fluoride, the concentration of said nickel fluoride being such that substantially no gassing occurs at the anode for a given temperature, pH, anode current density and agitation.

References Iited by the Examiner UNiTED STATES PATENTS 1,607,960 11/26 Madsen 204-49 2,313,756 3/43 Loose 204--49 2,453,757 11/48 Renzoni 20449 2,654,705 10/53 Case 20449 2,728,720 12/55 De Long 204-49 2,951,978 9/60 Dickson 204- 19 EGHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner. 

1. A METHOD OF ELECTROPLATING NICKEL COMPRISING THE STEPS OF: FORMING AN AQUEOUS BATH CONSISTING ESSENTIALLY OF NICKEL SULFATE; A FLUORIDE SALT SELECTED FROM THE GROUP CONSISTING OF NICKEL FLUORIDE, POTASSIUM FLUORIDE, AND SODIUM FLUORIDE, AND MIXTURES THEREOF; IMMERSING INTO SAID BATH AN ANODE OF SUBSTANTIALLY PURE UNTREATED ELECTROLYTIC NICKEL, IMMERSING INTO SAID BATH THE ARTICLE TO BE PLATED AS THE CATHODE; AND ELECTROPLATING SAID ARTICLE FROM SAID PURE NICKEL ANODE. 